Actually the term which we refer to as “computational problem complexity” has two different meanings which must be distinguished. On the first term, it means to an algorithm for solving instances of a problem: roughly stated, the computational complexity of an algorithm is the measure of how many basic steps the algorithm will need in the worst case for an instance or input of a given size. So, the number of steps is calculated as a function of that size. On the second term, it roughly refers to the difficulty of the problem whether it is easy or hard to solve.
I believe in this case we are referring to the first meaning of the complexity, hence the correct answer to fill in the blank would be:
“basic steps it requires”
